Sign in
12thPass logo
New chatPYQ LibraryDoubtsRank report
Sign in to see Recents

Your guest activity stays on this device

Sign in to save progress →
Sign in

Permutations and Combinations question

2025 · 23 Jan · Shift 2 · Q48
Guest · filters and generic practice availableBrowsing as a guest · PYQ filters and generic practice are available. Sign in only for personalised features and saved progress.
  1. PYQ Library
  2. /JEE Main
  3. /Mathematics
  4. /Permutations and Combinations
  5. /2025 · 23 Jan · Shift 2 · Q48

Permutations and Combinations question

2025 · 23 Jan · Shift 2 · Q48

JEE MainMathematicsPermutations and CombinationsNumerical+4 / −1
The number of ways, 5 boys and 4 girls can sit in a row so that either all the boys sit together or no two boys sit together, is ‾\underline{\hspace{2cm}}​.
Numerical answer
View written solutionFree

Correct answer: 17280

  1. Let us count the required arrangements in two separate cases:
  • Case 1: All 5 boys sit together.
  • Case 2: No two boys sit together.

Since these two cases cannot happen simultaneously (because if all 5 boys are together, then certainly boys are adjacent), we can add the counts directly.


  1. Case 1: All 5 boys sit together

Treat the 5 boys as one block.

Then we have:

  • 1 block of boys
  • 4 girls

So total objects to arrange = 555.

These can be arranged in: 5!5!5! ways.

Within the boys' block, the 5 boys can be arranged in: 5!5!5! ways.

Hence total arrangements in this case: 5!⋅5!=120⋅120=14400.5!\cdot 5! = 120\cdot 120 = 14400.5!⋅5!=120⋅120=14400.


  1. Case 2: No two boys sit together

First arrange the 4 girls.

This can be done in: 4!4!4! ways.

After arranging the girls, the available gaps are: _ G _ G _ G _ G _\_\ G\ \_\ G\ \_\ G\ \_\ G\ \__ G _ G _ G _ G _ So there are 555 gaps.

To ensure no two boys sit together, we must place the 5 boys in these 5 gaps, exactly one boy in each gap.

The 5 boys can be arranged in these 5 gaps in: 5!5!5! ways.

Thus total arrangements in this case: 4!⋅5!=24⋅120=2880.4!\cdot 5! = 24\cdot 120 = 2880.4!⋅5!=24⋅120=2880.


  1. Total required arrangements

14400+2880=17280.14400 + 2880 = 17280.14400+2880=17280.

So the required number of ways is: 17280\boxed{17280}17280​


  1. Comparison with stored correct answer

Stored correct answer = 172801728017280

Our derived answer = 172801728017280

Hence, the answer agrees with the stored correct answer.

PreviousNext

More from Permutations and Combinations

  • The number of 3 -digit numbers, that are divisible by 2 and 3 , but not divisible by 4 and 9 , is ​.2025 · Numerical
  • Group A consists of 7 boys and 3 girls, while group B consists of 6 boys and 5 girls. The number of ways, 4 boys and 4 girls can be invited for a picnic if 5 of them must be from group A and the remaining 3 from group B, is equal to :2025 · MCQ
  • Number of functions f:{1,2,…,100}→{0,1}, that assign 1 to exactly one of the positive integers less than or equal to 98 , is equal to ​.2025 · Numerical
  • Let nCr−1​=28,nCr​=56 and nCr+1​=70. Let A(4cost,4sint),B(2sint,−2cost) and C(3r−n,r2−n−1) be the vertices of a triangle ABC, where t is a parameter. If (3x−1)2+(3y)2=α…2025 · MCQ
  • The number of different 5 digit numbers greater than 50000 that can be formed using the digits 0 , 1,2,3,4,5,6,7, such that the sum of their first and last digits should not be more than 8 , is2025 · MCQ
  • The number of natural numbers, between 212 and 999, such that the sum of their digits is 15, is ​.2025 · Numerical
  • Let P be the set of seven digit numbers with sum of their digits equal to 11. If the numbers in P are formed by using the digits 1, 2 and 3 only, then the number of elements in the set P is :2025 · MCQ
  • The number of 6-letter words, with or without meaning, that can be formed using the letters of the word MATHS such that any letter that appears in the word must appear at least twice, is ​.2025 · Numerical